The process by which the mammalian immune system recognizes and reacts to foreign or alien materials is a complex one. An important facet of the system is the T-cell response. This response requires that T cells recognize and interact with complexes of cell surface molecules referred to as human leukocyte antigens (HLA) constituting the human major histocompatibility complex (MHC), and peptides. The peptides are derived from larger molecules, which are processed by the cells, which also present the HLA/MHC molecule. The interaction of T cells and complexes of HLA/peptide is restricted, requiring a T cell that is specific for a particular combination of an HLA molecule and a peptide. If a specific T cell is not present, there is no T-cell response even if its partner complex is present. Similarly, there is no response if the specific complex is absent, but the T cell is present.
The mechanism by which T cells recognize cellular abnormalities has also been implicated in cancer. E.g. in WO92/20356, a family of genes is disclosed which are processed into peptides which, in turn, are expressed on cells surfaces, and can lead to lysis of the tumour cells by specific CTLs. These genes are referred to as the MAGE family and are said to code for “tumour rejection antigen precursors” or “TRAP” molecules, and the peptides derived therefrom are referred to as “tumour rejection antigens” or “TRAs”.
In WO 94/05304, nonapeptides are disclosed which bind to the HLA-A1 molecule. The reference discloses that given the known specificity of particular peptides for particular HLA molecules, one should expect a particular peptide to bind one HLA molecule, but not others. This is significant, because different individuals possess different HLA phenotypes. As a result, while identification of a particular peptide as being a partner for a specific HLA molecule has diagnostic and therapeutic ramifications, these are only relevant for individuals with that particular HLA phenotype.
Several peptides presented by MHC molecules have been characterized and it has been found that some of these may carry posttranslational modifications possibly having an impact on the functionality of the HLA-peptide complex. Thus, a number of studies have associated alterations in the pattern of phosphorylation with malignant transformation. Furthermore, it has been shown that phosphorylation could have a neutral, negative or even a positive effect on peptide binding to class I MHC and that phosphopeptide-specific CTL, which discriminated between the phosphorylated and the non-phosphorylated versions of the peptide, could be generated, showing that such CTL most likely are part of the class I MHC-restricted CTL repertoire. Recently, it has been shown that phosphorylated peptides indeed are processed naturally and presented by MHC class I molecules in vivo. Additionally, the presence of phosphorylated peptides in extracts from isolated class I molecules from several different EBV-transformed B-cells has been established.
Thus, it is well established that peptide epitopes derived from tumor associated antigens (TAAs) can be recognized as antigens by cytotoxic T lymphocytes (CTLs) in the context of MHC molecules (1). However, although it is generally accepted that most if not all, tumours are antigenic, only a few are indeed immunogenic in the sense that tumour progression is readily controlled by the immune system.
To overcome this limitation, several immunotherapeutic trials have been initiated, e.g. vaccinations with TAA-derived peptides. For melanoma, the tumour for which the largest number of CTL-defined TAAs has been characterized, powerful CTL responses against antigens have been induced by vaccination and some patients experienced a complete remission of their disease (2,3). However, most of the peptide epitopes used in these vaccination trials are melanocyte specific, and these peptides cannot be applied for tumours of non-melanocyte origin. Furthermore, expression of these TAAs is heterogeneous among tumours from different patients and can even vary among metastases obtained from one patient. However, during the last couple of years a number of tumour specific peptide antigens, which are expressed in a number of different cancers, have been identified, i.e. HER-2 (4), Muc-1 (5) and telomerase (6).
It has also been shown that by proper manipulation tumor antigens present in tumors can be exposed to the immune system. Studies have shown that the CD8+ CTL arm of the immune response, alone or in combination with CD4+ Th cells, constitutes the primary anti-tumor effector arm of the adaptive immune response. Up till now the focus has mainly been on the CTL arm of the immune response. However, it is becoming more and more clear that the CD4 T cell response plays an essential role in tumor rejection, especially in the induction phase or in the extension of a CTL response in vivo. Consequently, the incorporation of class II-restricted tumor antigens into effective tumor vaccination protocols might increase the effectiveness of the vaccines.
Apoptosis is a genetic program of cellular suicide, and inhibition of apoptosis has been suggested to be an important mechanism involved in cancer formation by extending the life span of cells favouring the accumulation of transforming mutations (7). Survivin is a recently identified member of the family of inhibitors of apoptosis proteins (IAPs). In a global gene expression analysis of about 4 million transcripts, survivin was identified as one of the top genes invariably up-regulated in many types of cancer but not in normal tissue (8). Solid malignancies overexpressing survivin include lung, colon, breast, pancreas, and prostate cancer as well as hematopoietic malignancies (9). Additionally, series of melanoma and non-melanoma skin cancers have been reported to be invariably survivin positive (10,11). The overexpression of survivin in most human cancers suggests a general role of apoptosis inhibition in tumor progression, a notion substantiated by the observation that in the case of colorectal and bladder cancer, as well as neuroblastoma, expression of survivin was associated with an unfavourable prognosis. In contrast, survivin is undetectable in normal adult tissues. These characteristics qualify survivin as a suitable TAA for both diagnostic and therapeutic purposes.
Thus, during the last decade a large number of TAAs have been identified which are recognized by CTLs in a major histocompatibility complex (MHC)-restricted fashion. As survivin is overexpressed in most human cancers and inhibition of its function results in increased apoptosis, this protein may serve as a target for therapeutic CTL responses. The survivin protein and the potential diagnostic and therapeutic use hereof are disclosed in (8) and U.S. Pat. No. 6,245,523, which are incorporated herein by reference. Survivin is a 16.5 kDa cytoplasmic protein containing a single BIR and a highly charged carboxy-terminal coiled region instead of a RING finger, which inhibits apoptosis induced by growth factor (IL-3) withdrawal when transferred in B cell precursors. The gene coding for survivin is nearly identical to the sequence of Effector Cell Protease Receptor-1 (EPR-1), but oriented in the opposite direction, thus suggesting the existence of two separate genes duplicated in a head-to-head configuration. Accordingly, survivin can be described as an antisense EPR-1 product. Functionally, inhibition of survivin expression by up-regulating its natural antisense EPR-1 transcript results in massive apoptosis and decreased cell growth.
U.S. Pat. No. 6,245,523 discloses the isolation of purified survivin and it provides nucleic acid molecules that encode the survivin protein, and antibodies and other molecules that bind to survivin. U.S. Pat. No. 6,245,523 also discloses anti-apoptotically active fragments of the survivin protein and variants hereof wherein an amino acid residue has been inserted N- or C-terminal to, or within, the disclosed survivin sequence. It is specifically disclosed that such peptides should contain key functional residues required for apoptosis, i.e. Trp at position 67, Pro at position 73 and Cys at position 84.
The present invention is based on the discovery that MHC Class I restricted peptides can be derived from the survivin protein, which are capable of binding to MHC Class I HLA molecules and thereby eliciting both ex vivo and in situ CTL immune responses in patients suffering from a wide range of cancer diseases. These findings strongly suggest that survivin acts as a TRAP molecule, which is processed by cells into peptides having TRA functionality. Evidently, these findings open the way for novel therapeutic and diagnostic approaches which, due to the fact that survivin appears to be expressed universally by tumour cells, are generally applicable in the control of cancer diseases.